A compact engine is employed as a power source in an electric generator and a portable work tool such as a grass-trimmer, a brush cutter, a blower, a chain-saw, and a power cutter.
Such a conventional engine includes a cooling fan provided on one end of a crank shaft for cooling a cylinder. Rotation of the crank shaft causes the cooling fan to rotate, thereby generating cooling air for cooling the cylinder.
Japanese Patent Application. Publication No. H06-123243 discloses a mechanism in which a wind governor is employed to utilize cooling air for controlling operational states (rotation speed) of an engine. Specifically, a governor plate is disposed on an air flow path of the cooling air within a fan case. The governor plate is connected to a throttle valve shaft of a carburetor that controls a throttle opening in the carburetor. The governor plate is pivotally movable about this throttle valve shaft.
Specifically, in this wind governor, the throttle valve shaft is caused to rotate to decrease the throttle opening when a load decreases, a rotation speed increases, and wind power of cooling air becomes stronger. Conversely, the throttle valve shaft is caused to rotate to increase the throttle opening when the load increases, the rotation speed drops, and wind power of cooling air becomes weaker.
This mechanism is easily configured by simply connecting a small-sized governor plate (wind governor) to the throttle valve shaft and is therefore effective in various types of portable engine-powered work tools that require compact engines.